This invention relates to filter apparatus for removing contaminants from air.
The contaminants that are present in normal room air include dust particles, pollens, bacteria, viruses and various odoriferous molecules. It is frequently desirable to remove dust particles and pollens from the air in a particular room, for example because the occupant of the room is allergic to one or more of the contaminants. Furthermore, in a hospital operating room or a dentist's office, it is desirable to remove bacteria and viruses in order to prevent the spread of infection. Removal of odoriferous contaminants, such as hydrogen sulfide and sulfur dioxide, is desirable in order to make occupation of the room more pleasant.
It is known to use various types of mechanical and absorbent filter elements in portable fan-driven filters for removing contaminants from the air in a room. In particular, such filters are used to remove airborne dust.
It is also known to use ultraviolet light to kill airborne bacteria. For example, an ultraviolet bulb may be mounted in an air conditioning duct so that all the air that passes through the duct is irradiated. This is a form of filtration, since the bacteria's capacity to reproduce is removed. A disadvantage of this arrangement is that measures must be taken to remove dust from the air before it reaches the ultraviolet bulb, because otherwise dust is deposited on the bulb and impairs its efficiency. It is possible to use an electrostatic filter to extract dust particles from the air, but such filters are very expensive. Another expensive alternative is to use a HEPA (high efficiency particle arrestance) filter, but such a filter would have a relatively short useful life because of the large volume of air passing through the filter.
Molecular sieves can be used to remove certain species of molecules from the air. A typical molecular sieve is made from crystalline zeolite material and operates by adsorbing molecules that are smaller than a limit that depends on the crystal structure of the sieve material.